As one of pole measuring methods for analyzing a polycrystalline sample using an X-ray diffractometer, there is a pole measuring method for analyzing preferred orientation (texture) and the like of the sample by using a pole figure. The pole figure refers to a figure representing poles with respect to a specified lattice plane of crystallites constituting the sample by a polar net (a stereographic projection) as shown in FIG. 6. Here, the term “pole” signifies an intersection of the normal to a lattice plane with a projection sphere about the crystallites constituting the sample.
FIG. 5 is a schematic view explaining a conventional pole measuring method using a four-axis X-ray diffractometer.
As shown in FIG. 5, the sample S is rotated in directions of ω about an axis Ω, and is rotatable about an axis ψ in the surface Sa of the sample S. Also, the sample S is in-plane rotated about an axis Φ perpendicular to the sample surface Sa. These axes Ω, ψ, and Φ intersect one another at the origin on the sample surface Sa (generally at the center of the sample). An incident X-ray X0 is applied to the sample surface Sa at an incident angle θ along an equator plane. The setting of the incident angle θ is performed by the ω-rotation of the sample S. Here, the equator plane shown in FIG. 5 refers to a horizontal plane passing the origin O and perpendicular to the Ω-axis.
An X-ray detector 1 is mounted on a counter arm which rotates about the Ω-axis along the equator plane. In the pole measuring, the X-ray detector 1 is generally disposed at the symmetrical position on the equator plane which satisfies a Bragg's diffraction condition, that is, a position in the direction of a diffracting angle of an X-ray equal to the incident angle θ of the X-ray with respect to the sample surface Sa. Specifically, the X-ray detector 1 is positioned, by revolving the counter arm about the Ω-axis, at an angle of 2θ with respect to the incident X-ray X0 which is applied to the sample at the incident angle θ.
The sample S is rotated about the ψ-axis in minute angle units (tilting angle α), and is in-plane rotated about the Φ-axis at each predetermined angle. In this manner, with each of the tilting angles α and each of the in-plane rotation angles β as parameters, a diffracted X-ray X1 which is a Bragg diffraction by the sample surface Sa is measured by the X-ray detector 1, disposed on the equator plane and fixed at a position at an angle of 2θ with respect to the direction of the incident X-ray X0.
By representing these measurement results on a graph named as a polar net, a pole figure is produced. In the polar net, the tilting angles α are shown in radial directions thereof, and the tilting angle α is defined so that α=90° at the center thereof, and that α=0° at the outer periphery thereof. When the sample surface Sa is perpendicular to the equator plane, the tilting angle α is 90°. In the polar net, the in-plane rotation angle β is shown in the circumferential direction thereof.
FIG. 7 shows an example of pole figure with a pole of (111) of cold-rolled CuZn in which the ratio of Cu to Zn is 70 to 30.
In the conventional pole measuring, an X-ray beam of line-shaped cross-section is used as an incident X-ray, and therefore, when the tilting angle becomes small, that is, when the sample surface is tilted to a position near the horizontal plane in FIG. 5, the irradiation width of the incident X-ray with respect to the sample surface enlarges, and only one portion of the incident X-ray contributes to diffraction, thereby significantly reducing the intensity of the incident X-ray. As a result, in a low region of the tilting angle α, a reflection method, in which a diffracted X-ray is reflected from the sample surface outwardly, does not allow the poles to be measured.
Accordingly, in a low angle region, a transmission method, in which a diffracted X-ray transmitted through the sample is measured, has been hitherto used for a pole measuring. In general, the reflection method has been used when the tilting angle α is in a range of 90° to 25°, while the transmission method has been used when the tilting angle α is in a range of 25° to 0°.
However, in the measurement by transmission, the intensity of a transmitted X-ray is reduced by the self-absorption. This has raised a problem that, since a sufficient intensity of X-ray cannot be obtained with respect to thick samples or samples formed on a substrate, extremely thin samples alone have been measurable. Hitherto, therefore, the pole measuring with respect to these thick samples and thin-film samples formed on a substrate have not been possible in a low region of the tilting angle α.